ON LIGHT. 345 



These observations lead us to conclude, that light acquires. Light thus 



under these circumstances, properties independent of its direc- acquires pro- 



• 1 11 ,. . . ■ . I perties relative 



tion, with regard to the surface which reflects it, but exclusively to the sides of 



relative to the sides of the vertical ray, which are here the same the ray. 

 for the north and south sides of the ray, but difl:erent with re- 

 gardto the east and west sides. 



By giving to these sides the name of poles, Malus has given Modification, 

 the name of po/amai!ion, to that modification which imparts which the au- 

 ... ... , . , . , , thor calls pola- 



properties to light, which are relative to these poles. And he risation. 



says, that he has hesitated to admit of that term in the de- 

 scription of the natural effects now under consideration, until 

 the variety of the phenomena obliged him to make use of it. 



Let us again, says he, consider the apparatus of which we The Hght 

 have been speaking. If to the solar ray which has passed ^r^"*^"^!/'^^ 

 through the first glass, and of which a part has been reflected, first glass is 

 a silvered glass be presented, which shall reflect it perpen- polarised dif- 

 dicularly downwards, a second vertical ray will be obtained, ^'^^^ ^' 

 which has properties similar to the first, but in a directly oppo- 

 site manner. 



If a glass be presented to this ray, forming with its direction -pj^^ reflection 



an angle of 35° 25', and if, without changing this inclination, will i^e much 



its faces be alternately turned towards the north and south, e^ist ^^""^ ^"j"^" '^^ 

 ■' ' second fjlass 



and west, the following phenomena will be observed. There faces north or 



will always be a certain quantity of light reflected by the second ®°'^'^' 



glass, but this q-ianiity will be much less when the faces are 



turned towards the north and south, than when they are turned 



towards the east and west. 



In the first vertical ray, exactly the contrary may be observed, which is di- 



The viinim urn of reflected Wgui look place when the second '"^^^'y ^''"'"'"T 



, , , , , . to what hap- 



glass was turned towards the east or the west. Thus, in abstract- pens with the 



ing from the second ray the quantity of light which comports first vertical 

 itself like a common ray, and which is reflected equally under '^^^* 

 both circumstances, it will be seen, that this ray contains ano- 

 ther portion of light, which is polarised in a manner exactly 

 contrary to that of the vertical ray reflected by the first glass. 



In this experiment a silvered mirror was used, merely in ^hg gHrered 

 order to dispose the two rays parallel to each other, and under glass is not re- 

 the same circumstances, in order to render the explanation more has'lhtie^effect 

 clear. The action of metallic surfaces being very weak with on the polari- 



, „„^j «ation. 



regard 



